This section provides background information related to the present disclosure which is not necessarily prior art.
Typical LLC resonant converters include power switches and a control circuit that adjusts a switching frequency of the power switches to regulate an output voltage of the LLC resonant converters. Preferably, the LLC resonant converters are operated in critically discontinuous conduction mode so that current through resonant elements (e.g., commonly referred to as a resonant inductor Lr and a resonant capacitor Cr) in the LLC resonant converters is zero for an infinitely small amount of time in each switching period. As a result, the power switches may be switched at zero current thereby optimizing efficiency in the LLC resonant converters. To achieve critically discontinuous conduction mode, the switching frequency of the power switches is substantially equal to the resonant frequency of the resonant elements.
Generally, the LLC resonant converters are designed to operate in critically discontinuous conduction mode when a load operates at a fixed load condition (e.g., 50% load, etc.). This ensures the switching frequency of the power switches are not substantially adjusted when regulating the output voltage of the LLC resonant converters as explained above.